net/dccp/ackvec.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  net/dccp/ackvec.c
   4  *
   5  *  An implementation of Ack Vectors for the DCCP protocol
   6  *  Copyright (c) 2007 University of Aberdeen, Scotland, UK
   7  *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
   8  */
   9 #include "dccp.h"
  10 #include <linux/kernel.h>
  11 #include <linux/slab.h>
  12 #include <linux/export.h>
  13
  14 static struct kmem_cache *dccp_ackvec_slab;
  15 static struct kmem_cache *dccp_ackvec_record_slab;
  16
  17 struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority)
  18 {
  19         struct dccp_ackvec *av = kmem_cache_zalloc(dccp_ackvec_slab, priority);
  20
  21         if (av != NULL) {
  22                 av->av_buf_head = av->av_buf_tail = DCCPAV_MAX_ACKVEC_LEN - 1;
  23                 INIT_LIST_HEAD(&av->av_records);
  24         }
  25         return av;
  26 }
  27
  28 static void dccp_ackvec_purge_records(struct dccp_ackvec *av)
  29 {
  30         struct dccp_ackvec_record *cur, *next;
  31
  32         list_for_each_entry_safe(cur, next, &av->av_records, avr_node)
  33                 kmem_cache_free(dccp_ackvec_record_slab, cur);
  34         INIT_LIST_HEAD(&av->av_records);
  35 }
  36
  37 void dccp_ackvec_free(struct dccp_ackvec *av)
  38 {
  39         if (likely(av != NULL)) {
  40                 dccp_ackvec_purge_records(av);
  41                 kmem_cache_free(dccp_ackvec_slab, av);
  42         }
  43 }
  44
  45 /**
  46  * dccp_ackvec_update_records  -  Record information about sent Ack Vectors
  47  * @av:         Ack Vector records to update
  48  * @seqno:      Sequence number of the packet carrying the Ack Vector just sent
  49  * @nonce_sum:  The sum of all buffer nonces contained in the Ack Vector
  50  */
  51 int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seqno, u8 nonce_sum)
  52 {
  53         struct dccp_ackvec_record *avr;
  54
  55         avr = kmem_cache_alloc(dccp_ackvec_record_slab, GFP_ATOMIC);
  56         if (avr == NULL)
  57                 return -ENOBUFS;
  58
  59         avr->avr_ack_seqno  = seqno;
  60         avr->avr_ack_ptr    = av->av_buf_head;
  61         avr->avr_ack_ackno  = av->av_buf_ackno;
  62         avr->avr_ack_nonce  = nonce_sum;
  63         avr->avr_ack_runlen = dccp_ackvec_runlen(av->av_buf + av->av_buf_head);
  64         /*
  65          * When the buffer overflows, we keep no more than one record. This is
  66          * the simplest way of disambiguating sender-Acks dating from before the
  67          * overflow from sender-Acks which refer to after the overflow; a simple
  68          * solution is preferable here since we are handling an exception.
  69          */
  70         if (av->av_overflow)
  71                 dccp_ackvec_purge_records(av);
  72         /*
  73          * Since GSS is incremented for each packet, the list is automatically
  74          * arranged in descending order of @ack_seqno.
  75          */
  76         list_add(&avr->avr_node, &av->av_records);
  77
  78         dccp_pr_debug("Added Vector, ack_seqno=%llu, ack_ackno=%llu (rl=%u)\n",
  79                       (unsigned long long)avr->avr_ack_seqno,
  80                       (unsigned long long)avr->avr_ack_ackno,
  81                       avr->avr_ack_runlen);
  82         return 0;
  83 }
  84
  85 static struct dccp_ackvec_record *dccp_ackvec_lookup(struct list_head *av_list,
  86                                                      const u64 ackno)
  87 {
  88         struct dccp_ackvec_record *avr;
  89         /*
  90          * Exploit that records are inserted in descending order of sequence
  91          * number, start with the oldest record first. If @ackno is `before'
  92          * the earliest ack_ackno, the packet is too old to be considered.
  93          */
  94         list_for_each_entry_reverse(avr, av_list, avr_node) {
  95                 if (avr->avr_ack_seqno == ackno)
  96                         return avr;
  97                 if (before48(ackno, avr->avr_ack_seqno))
  98                         break;
  99         }
 100         return NULL;
 101 }
 102
 103 /*
 104  * Buffer index and length computation using modulo-buffersize arithmetic.
 105  * Note that, as pointers move from right to left, head is `before' tail.
 106  */
 107 static inline u16 __ackvec_idx_add(const u16 a, const u16 b)
 108 {
 109         return (a + b) % DCCPAV_MAX_ACKVEC_LEN;
 110 }
 111
 112 static inline u16 __ackvec_idx_sub(const u16 a, const u16 b)
 113 {
 114         return __ackvec_idx_add(a, DCCPAV_MAX_ACKVEC_LEN - b);
 115 }
 116
 117 u16 dccp_ackvec_buflen(const struct dccp_ackvec *av)
 118 {
 119         if (unlikely(av->av_overflow))
 120                 return DCCPAV_MAX_ACKVEC_LEN;
 121         return __ackvec_idx_sub(av->av_buf_tail, av->av_buf_head);
 122 }
 123
 124 /**
 125  * dccp_ackvec_update_old  -  Update previous state as per RFC 4340, 11.4.1
 126  * @av:         non-empty buffer to update
 127  * @distance:   negative or zero distance of @seqno from buf_ackno downward
 128  * @seqno:      the (old) sequence number whose record is to be updated
 129  * @state:      state in which packet carrying @seqno was received
 130  */
 131 static void dccp_ackvec_update_old(struct dccp_ackvec *av, s64 distance,
 132                                    u64 seqno, enum dccp_ackvec_states state)
 133 {
 134         u16 ptr = av->av_buf_head;
 135
 136         BUG_ON(distance > 0);
 137         if (unlikely(dccp_ackvec_is_empty(av)))
 138                 return;
 139
 140         do {
 141                 u8 runlen = dccp_ackvec_runlen(av->av_buf + ptr);
 142
 143                 if (distance + runlen >= 0) {
 144                         /*
 145                          * Only update the state if packet has not been received
 146                          * yet. This is OK as per the second table in RFC 4340,
 147                          * 11.4.1; i.e. here we are using the following table:
 148                          *                     RECEIVED
 149                          *                      0   1   3
 150                          *              S     +---+---+---+
 151                          *              T   0 | 0 | 0 | 0 |
 152                          *              O     +---+---+---+
 153                          *              R   1 | 1 | 1 | 1 |
 154                          *              E     +---+---+---+
 155                          *              D   3 | 0 | 1 | 3 |
 156                          *                    +---+---+---+
 157                          * The "Not Received" state was set by reserve_seats().
 158                          */
 159                         if (av->av_buf[ptr] == DCCPAV_NOT_RECEIVED)
 160                                 av->av_buf[ptr] = state;
 161                         else
 162                                 dccp_pr_debug("Not changing %llu state to %u\n",
 163                                               (unsigned long long)seqno, state);
 164                         break;
 165                 }
 166
 167                 distance += runlen + 1;
 168                 ptr       = __ackvec_idx_add(ptr, 1);
 169
 170         } while (ptr != av->av_buf_tail);
 171 }
 172
 173 /* Mark @num entries after buf_head as "Not yet received". */
 174 static void dccp_ackvec_reserve_seats(struct dccp_ackvec *av, u16 num)
 175 {
 176         u16 start = __ackvec_idx_add(av->av_buf_head, 1),
 177             len   = DCCPAV_MAX_ACKVEC_LEN - start;
 178
 179         /* check for buffer wrap-around */
 180         if (num > len) {
 181                 memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, len);
 182                 start = 0;
 183                 num  -= len;
 184         }
 185         if (num)
 186                 memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, num);
 187 }
 188
 189 /**
 190  * dccp_ackvec_add_new  -  Record one or more new entries in Ack Vector buffer
 191  * @av:          container of buffer to update (can be empty or non-empty)
 192  * @num_packets: number of packets to register (must be >= 1)
 193  * @seqno:       sequence number of the first packet in @num_packets
 194  * @state:       state in which packet carrying @seqno was received
 195  */
 196 static void dccp_ackvec_add_new(struct dccp_ackvec *av, u32 num_packets,
 197                                 u64 seqno, enum dccp_ackvec_states state)
 198 {
 199         u32 num_cells = num_packets;
 200
 201         if (num_packets > DCCPAV_BURST_THRESH) {
 202                 u32 lost_packets = num_packets - 1;
 203
 204                 DCCP_WARN("Warning: large burst loss (%u)\n", lost_packets);
 205                 /*
 206                  * We received 1 packet and have a loss of size "num_packets-1"
 207                  * which we squeeze into num_cells-1 rather than reserving an
 208                  * entire byte for each lost packet.
 209                  * The reason is that the vector grows in O(burst_length); when
 210                  * it grows too large there will no room left for the payload.
 211                  * This is a trade-off: if a few packets out of the burst show
 212                  * up later, their state will not be changed; it is simply too
 213                  * costly to reshuffle/reallocate/copy the buffer each time.
 214                  * Should such problems persist, we will need to switch to a
 215                  * different underlying data structure.
 216                  */
 217                 for (num_packets = num_cells = 1; lost_packets; ++num_cells) {
 218                         u8 len = min_t(u32, lost_packets, DCCPAV_MAX_RUNLEN);
 219
 220                         av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, 1);
 221                         av->av_buf[av->av_buf_head] = DCCPAV_NOT_RECEIVED | len;
 222
 223                         lost_packets -= len;
 224                 }
 225         }
 226
 227         if (num_cells + dccp_ackvec_buflen(av) >= DCCPAV_MAX_ACKVEC_LEN) {
 228                 DCCP_CRIT("Ack Vector buffer overflow: dropping old entries");
 229                 av->av_overflow = true;
 230         }
 231
 232         av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, num_packets);
 233         if (av->av_overflow)
 234                 av->av_buf_tail = av->av_buf_head;
 235
 236         av->av_buf[av->av_buf_head] = state;
 237         av->av_buf_ackno            = seqno;
 238
 239         if (num_packets > 1)
 240                 dccp_ackvec_reserve_seats(av, num_packets - 1);
 241 }
 242
 243 /**
 244  * dccp_ackvec_input  -  Register incoming packet in the buffer
 245  */
 246 void dccp_ackvec_input(struct dccp_ackvec *av, struct sk_buff *skb)
 247 {
 248         u64 seqno = DCCP_SKB_CB(skb)->dccpd_seq;
 249         enum dccp_ackvec_states state = DCCPAV_RECEIVED;
 250
 251         if (dccp_ackvec_is_empty(av)) {
 252                 dccp_ackvec_add_new(av, 1, seqno, state);
 253                 av->av_tail_ackno = seqno;
 254
 255         } else {
 256                 s64 num_packets = dccp_delta_seqno(av->av_buf_ackno, seqno);
 257                 u8 *current_head = av->av_buf + av->av_buf_head;
 258
 259                 if (num_packets == 1 &&
 260                     dccp_ackvec_state(current_head) == state &&
 261                     dccp_ackvec_runlen(current_head) < DCCPAV_MAX_RUNLEN) {
 262
 263                         *current_head   += 1;
 264                         av->av_buf_ackno = seqno;
 265
 266                 } else if (num_packets > 0) {
 267                         dccp_ackvec_add_new(av, num_packets, seqno, state);
 268                 } else {
 269                         dccp_ackvec_update_old(av, num_packets, seqno, state);
 270                 }
 271         }
 272 }
 273
 274 /**
 275  * dccp_ackvec_clear_state  -  Perform house-keeping / garbage-collection
 276  * This routine is called when the peer acknowledges the receipt of Ack Vectors
 277  * up to and including @ackno. While based on on section A.3 of RFC 4340, here
 278  * are additional precautions to prevent corrupted buffer state. In particular,
 279  * we use tail_ackno to identify outdated records; it always marks the earliest
 280  * packet of group (2) in 11.4.2.
 281  */
 282 void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno)
 283 {
 284         struct dccp_ackvec_record *avr, *next;
 285         u8 runlen_now, eff_runlen;
 286         s64 delta;
 287
 288         avr = dccp_ackvec_lookup(&av->av_records, ackno);
 289         if (avr == NULL)
 290                 return;
 291         /*
 292          * Deal with outdated acknowledgments: this arises when e.g. there are
 293          * several old records and the acks from the peer come in slowly. In
 294          * that case we may still have records that pre-date tail_ackno.
 295          */
 296         delta = dccp_delta_seqno(av->av_tail_ackno, avr->avr_ack_ackno);
 297         if (delta < 0)
 298                 goto free_records;
 299         /*
 300          * Deal with overlapping Ack Vectors: don't subtract more than the
 301          * number of packets between tail_ackno and ack_ackno.
 302          */
 303         eff_runlen = delta < avr->avr_ack_runlen ? delta : avr->avr_ack_runlen;
 304
 305         runlen_now = dccp_ackvec_runlen(av->av_buf + avr->avr_ack_ptr);
 306         /*
 307          * The run length of Ack Vector cells does not decrease over time. If
 308          * the run length is the same as at the time the Ack Vector was sent, we
 309          * free the ack_ptr cell. That cell can however not be freed if the run
 310          * length has increased: in this case we need to move the tail pointer
 311          * backwards (towards higher indices), to its next-oldest neighbour.
 312          */
 313         if (runlen_now > eff_runlen) {
 314
 315                 av->av_buf[avr->avr_ack_ptr] -= eff_runlen + 1;
 316                 av->av_buf_tail = __ackvec_idx_add(avr->avr_ack_ptr, 1);
 317
 318                 /* This move may not have cleared the overflow flag. */
 319                 if (av->av_overflow)
 320                         av->av_overflow = (av->av_buf_head == av->av_buf_tail);
 321         } else {
 322                 av->av_buf_tail = avr->avr_ack_ptr;
 323                 /*
 324                  * We have made sure that avr points to a valid cell within the
 325                  * buffer. This cell is either older than head, or equals head
 326                  * (empty buffer): in both cases we no longer have any overflow.
 327                  */
 328                 av->av_overflow = 0;
 329         }
 330
 331         /*
 332          * The peer has acknowledged up to and including ack_ackno. Hence the
 333          * first packet in group (2) of 11.4.2 is the successor of ack_ackno.
 334          */
 335         av->av_tail_ackno = ADD48(avr->avr_ack_ackno, 1);
 336
 337 free_records:
 338         list_for_each_entry_safe_from(avr, next, &av->av_records, avr_node) {
 339                 list_del(&avr->avr_node);
 340                 kmem_cache_free(dccp_ackvec_record_slab, avr);
 341         }
 342 }
 343
 344 /*
 345  *      Routines to keep track of Ack Vectors received in an skb
 346  */
 347 int dccp_ackvec_parsed_add(struct list_head *head, u8 *vec, u8 len, u8 nonce)
 348 {
 349         struct dccp_ackvec_parsed *new = kmalloc(sizeof(*new), GFP_ATOMIC);
 350
 351         if (new == NULL)
 352                 return -ENOBUFS;
 353         new->vec   = vec;
 354         new->len   = len;
 355         new->nonce = nonce;
 356
 357         list_add_tail(&new->node, head);
 358         return 0;
 359 }
 360 EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_add);
 361
 362 void dccp_ackvec_parsed_cleanup(struct list_head *parsed_chunks)
 363 {
 364         struct dccp_ackvec_parsed *cur, *next;
 365
 366         list_for_each_entry_safe(cur, next, parsed_chunks, node)
 367                 kfree(cur);
 368         INIT_LIST_HEAD(parsed_chunks);
 369 }
 370 EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_cleanup);
 371
 372 int __init dccp_ackvec_init(void)
 373 {
 374         dccp_ackvec_slab = kmem_cache_create("dccp_ackvec",
 375                                              sizeof(struct dccp_ackvec), 0,
 376                                              SLAB_HWCACHE_ALIGN, NULL);
 377         if (dccp_ackvec_slab == NULL)
 378                 goto out_err;
 379
 380         dccp_ackvec_record_slab = kmem_cache_create("dccp_ackvec_record",
 381                                              sizeof(struct dccp_ackvec_record),
 382                                              0, SLAB_HWCACHE_ALIGN, NULL);
 383         if (dccp_ackvec_record_slab == NULL)
 384                 goto out_destroy_slab;
 385
 386         return 0;
 387
 388 out_destroy_slab:
 389         kmem_cache_destroy(dccp_ackvec_slab);
 390         dccp_ackvec_slab = NULL;
 391 out_err:
 392         DCCP_CRIT("Unable to create Ack Vector slab cache");
 393         return -ENOBUFS;
 394 }
 395
 396 void dccp_ackvec_exit(void)
 397 {
 398         kmem_cache_destroy(dccp_ackvec_slab);
 399         dccp_ackvec_slab = NULL;
 400         kmem_cache_destroy(dccp_ackvec_record_slab);
 401         dccp_ackvec_record_slab = NULL;
 402 }